Thank you kiev for the detailed information. That was what I needed. I'll try to remove the MCU and check if there are some faulty elements in the circuit. The car cannot start because the ECU can't measure the voltage of the capacitor.

I'll try to take some measurements and see if I can find the culprit that messes with the measurement. It will be hard to measure and debug the circuit. I hope that I don't blow anything and fry the inverter board. Probably I should look for someone with more experience in these kind of things.

If something wrong happens I'll have to go by Lic's steps or to find another way to put a custom MCU and try to make it work.

I hope Lic manages to fix his problem with the new MCU and get back on the road.

Thank you kirq4e for the follow up with your solution. What month was your car built according to the label on the door jam. Or what is the VIN, to search for recall notices.

That chip is an op amp made by Analog Devices, AD8677. It is used on the little hybrid board soldered to the main board.

The hybrid is an isolation amplifier board made by Nihon Pulse Industry, ISA215, used to measure the high voltage of the pack and isolate it from the low level logic control circuits.

My 2012 had these same symptoms with this DTC code but i wasn't as deep into the circuits as now. My car was included in a limited recall to replace the MCU and the problem was solved.

i think the recall indicated an issue with insulation or something that was leaking current causing the DTC, but now my guess is that a failure such as this on the ISA was the cause of the limited recall.

How did they know to limit the recall to just a few cars within a month's build date? --Because there is a lot code number in white ink stamped over the coating on the ISA board. So very easy to trace which cars had the bad batch.

I'm really happy with the car, but the joy was short. The problem appeared again. I drove the car home, charged it. Showed me 111 km estimated range which surprised me. Yesterday I started my daily routine but at the first stop the check engine light lighted again and couldn't go into Ready. Now the car is back in the service centre and the guys will try to find the real fault that is causing the issue.

I'm not sure which month the car was built but the first registration is 01.2011. The VIN is VF71NZKZZBU900242. I couldn't find if it is in the recall notice. The original Citroen service centre told me only for a recall about the passenger airbag which already waits for me to take the car.

If the problem cannot be fixed the only thing left is to get a second hand MCU and try to move the VIN encoded chips.

Did yall check the other components in the schematic, such as the photocoupler PC7 and the FET2? What about the value of the resistors in the voltage divider, and all the little capacitors?

If the FET2 were slightly turned ON by leakage thru the PC7, then it could pull the voltage down by 8-10 volts with just a small current (~20mA) thru the large silver bleed resistor.

One troubleshooting test might be to open the circuit to the FET by disconnecting from the board the CN5 connector to the bleed resistor--now there is no leakage path in that leg. It will cause a slower bleed down of the 800uF cap and that might throw a different code, but at least it might allow it to go to READY if the FET leg is the source of the leakage.

Another idea is to replace the entire ISA215N hybrid board. The op amp is one component on that board, but there are several more, any of which could disrupt the function of the isolation amplifier. But i don't think it could pull down the capacitor voltage such as current thru the bleed resistor would.

I'm happy to share with you that the problem is fixed. The guy changed almost everything on the schema - the photocoupler, resistors and FET2. The problem appeared when the car gets slightly warmer after a few kilometers of driving. It appears that some of the components were changing their characteristics when the temperature gets a little higher. He said that he measured all of the resistors and they seemed to be OK but he decided to replace them.

So now the car is working fine. Managed to drive 35 km and 30 on the GOM. Today after I charged it the GOM displays 123 km of range which is more than enought for my daily driving. Probably the car will be charged once 2-3 days.

Thank you very much kiev for your help. Lic I hope you can fix your problem sooner.

It looks to me that there are 2 legs in that circuit, either of which could cause this problem.

One is a real voltage drop in the path involving the photocoupler, FET2 and the bleed resistor.

The other is an error (thermally-induced) in the voltage measurement leg feeding into the ISA215 hybrid board used to sense the HV.

Since the issue seems to be thermally induced and is not a permanent failure, and you thought replacing the op amp on the hybrid board fixed it (in the measurement leg), then either the series resistor string or the little chip capacitors would be good suspects. i hope he replaced the caps along with the resistors.

Those little ceramic chip capacitors can get stressed and crack at the solder joint, then get leaky and recover in thermal cycling. The little chip resistors could change value under thermal cycling, but it is a less common failure in my experience.

They put 3 caps in parallel, likely as a redundancy against failure, but there should have also been a series string to be effective. Tesla does this on their battery cell voltage measuring circuit.

Hi guys. I see kirq4e fixed his car. it is very good. I was not able look my car yet. My mechanic sold his shop and can't help me any more. So It is look like I need to repair my hybrid board or I need to find out if I can just change eeprom chip from my inverter board. My question is - is it difficult to remove mcu from a car to get access to inverter board? Can I do it by myself in garage? I am sure I can do it in shop by myself, but I don't have access in shop anymore.

i think you should be able to do it in your garage fairly easily. The 2 coolant lines will likely be the messy part, then there are two small control connectors, a small connector on the temperature sensor, one big orange connector across the front from the DC/DC, and 5 large wires for HV--two from the pack and three to the motor, underneath the access cover (need a T30 Torqs screwdriver/bit). Two bolts thru flanges toward the front and one flange at the rear, then it comes out. flip it over on your work bench and remove the cover bolts--you're in like flint, and Bob's your uncle!